Project Summary/Abstract Periodontal disease is characterized by destruction of the hard and soft tissues that comprise the periodontium. This destruction translates to a degradation of the extracellular matrices (ECM), which is mediated by bacterial proteases, host-derived matrix metalloproteinases (MMPs), and other proteases released by host tissues and immune cells. Furthermore, pathogenic microbes are a catalyst for periodontal disease pathogenesis since the development of a dysbiosis of the microbiome enhances a persistent immune response. These bacterial pathogens interact with host tissue and thereby trigger adverse cellular functions, including a heightened immune response, tissue destruction, and tissue migration. One implicated bacteria, the oral spirochete, Treponema denticola (T. denticola or Td), is highly associated with periodontal disease (5). We?ve demonstrated that a Td outer membrane protein complex called dentilisin, contributes to the chronic activation of pro-MMP-2 in periodontal ligament (PDL) cells (26,27). Dentilisin exposure also triggers increased expression levels of activators and effectors of active MMP-2 in PDL cells. Despite these advances, there is no mechanism known for dentilisin-induced MMP-2 activation or PDL cytopathic behaviors leading to disease, or potential treatment. One possible therapeutic to combat these interactions is nisin. Nisin is a naturally occurring bacteriocin, widely used food preservative, and probiotic agent naturally made by bacterial species similar to those in the gut and oral cavity. Our lab demonstrated that nisin is an effective anti-microbial against key periodontopathic bacteria at low concentrations, including Td, with the potential to disrupt oral biofilm formation in vitro (11). Importantly, although most nisin related literature documents its role against gram-positive bacteria, our published work (11) highlights its efficacy against gram-negative bacteria. Furthermore, nisin at low concentrations is also more effective against certain oral pathogenic versus commensal bacteria; making it a potentially useful and selective agent for oral applications. Proper clearance of Td may provide a more symbiotic microbiome and ?reset? homeostatic conditions needed for repair, remodeling or regeneration of the periodontium. Thus, the main hypotheses of this proposal are that T. denticola interactions with PDL cells mediate adverse effects on homeostasis and cellular functions leading to a compromised cellular phenotype. Additionally, nisin is a potential therapeutic for abrogating these effects. This hypothesis will be tested in the following specific aims: 1) Determine the mechanism of dentilisin-induced activation of pro- MMP-2 in PDL cells; 2) Characterize the effects of T. denticola(Td) challenge on PDL cell processes and differentiation; 3) Determine whether sub-antimicrobial doses of nisin can abrogate Td/dentilisin-mediated activation of MMP-2 in PDL cells. Success of this proposal will provide molecular evidence for a mechanism of Td-mediated adverse cytopathic effects leading to characteristics of severe periodontitis; as well as evidence on nisin as a potential therapeutic for reducing or reversing Td-mediated periodontopathic processes in vitro.